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Search for (semistable) charged heavy particles using the ionization in the Pixel Detector

Search for (semistable) charged heavy particles using the ionization in the Pixel Detector A.Gaudiello 1 , C. Gemme 1 , G.Gagliardi 1 , E. Guido 1 , S. Passaggio 1 , L. Rossi 1 , C. Schiavi 1 1 INFN Genova Last update at the RPVLL meeting: https://indico.cern.ch/event/276607.

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Search for (semistable) charged heavy particles using the ionization in the Pixel Detector

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  1. Search for (semistable) charged heavy particles using the ionization in the Pixel Detector A.Gaudiello1, C. Gemme1, G.Gagliardi1, E. Guido1, S. Passaggio1, L. Rossi1, C. Schiavi1 1INFN Genova Last update at the RPVLL meeting: https://indico.cern.ch/event/276607

  2. Motivations for the searches with dE/dx • The ATLAS Pixel detector is able to measure the particle ionization in the very first cm of the trajectory and to tag tracks that have high release due to low bg particles. • The measurement is possible if the track is reconstructed and it is not sensitive to possible decays or interactions with material after the silicon layers. • CMS analysis only for stable, using ID only, ID+MS, MS only: doi:10.1007/JHEP07(2013)122 • Bethe-Bloch empirical fit of low mass particles allows to measure the particle mass from its energy release and momentum measurement • This calibration done in 2010 is very stable over the time. Proton mass

  3. Pixel-only Analysis 2012 • Benchmark signals: • Stablesquarks and gluinos R-hadrons, as in 2011, in extended mass range 200-1700 GeV; • Metastablesquarks and gluinos R-hadrons with lifetime 10,1,0.1,0.01, 0.001 ns and mass 400,600,800, 1000 GeV and decaying in a heavy or light neutralino. • Stable(100-800 GeV) and metastableCharginos(same samples as kinked tracks analysis, lifetime 0.3-1 ns). • Two main changes in 2012 wrt 2011 analysis: • In the DESDM RPVLL stream, the online skimming of the JetTauEtmiss stream has raised the high-pT track threshold from 50 to 80 GeV. • The un-prescaled triggers have changed wrt to 2011. • EF_xe80T_tclcw_loose; // All data periods

  4. Stable squarks and gluinos R-hadrons 49% 31% 20%

  5. Trigger selection and Efficiency • Trigger: • EF_xe80T_tclcw_loose triggers ~ 98% of the OR of the unprescaled MET triggers in signal events. • We prefer to adopt one single trigger for the full data period to make the study of the systematics simpler. • Trigger efficiency is ~17% on a wide range of masses (slightly larger than in 2011). 2012 2011

  6. Event Selection Cuts have been revised to optimize S/√B and populate the bkg samples. • Event level (after RPVLL filter and squeezing): • GRL* • offline confirmation of the MET trigger: Etmiss RefFinal > 130 GeV (was 80) • at least 1 primary vertex (PV) with at least 5 tracks • SUSY recommended event cleaning • Track level (at least one track with) • High-pT: pT>80 GeV, primary, n.Pixel hits >=3, nBLayer hits >=1 and n.SCT hits >=6 • Isolated: no primary with pT>1 GeV in a cone of radius ΔR<0.25 • Electron veto, • p-cuts: p>150 GeV & Δp/p<50% (was p>100 GeV) • High ionization: dE/dx > 1.800 - 0.055|η|+ 0.129|η|2 -0.037|η|3 MeV/g cm-2 * (A-G)data12_8TeV.periodAllYear_DetStatus-v54-pro13-04_DQDefects-00-00-33_PHYS_StandardGRL_All_Good.xml (H-L)data12_8TeV.periodAllYear_DetStatus-v61-pro14-02_DQDefects-00-01-00_PHYS_StandardGRL_All_Good.xml

  7. Small sensitivity to Pile-up Period J Being the pixel detector at high granularity, it is not very sensitive to pile-up. Anyhow MC needs to be properly reweighted with PU: effect is mainly on the skimming of the track. high low

  8. MC 2011 gluino 1000 GeV MC 2012 gluino 1000 GeV data 2012 (period J, ~3ifb) data 2011 (5ifb) * * Squeezed = Ef_xexx_yy and track pT>80 GeV, 2 pix, 6 SCT • Slight increase in signal efficiency (7.7% vs 5.8%) • Higher rejection for background (314 vs 40*5fib/3ifb candidates)

  9. Outlook for stable • We are studying and revising the definition of the background samples. Analysis cuts could slightly change to allow enough statistics in the bkg samples. • Bkg1 (low ionization) as data but dE/dx <1.8 • Bkg2(low momentum) as data but p<150 GeV and pT>10 GeV • Next-to-next: • Study systematics. • Move to analysis for stable charginos.

  10. Metastable squarks and gluinos R-hadrons R-hadrons Decay in neutralinos (either close to the R-hadron mass or lighter). Current selection is pretty efficient on MET. Inefficiency comes if lifetime is too short to generate a reconstructable track.

  11. “Reconstructable” charged R-hadrons • Ratio of • Charged R-hadrons associated (DR<0.01) to a track with pT>5 GeV(no other request!) and generated charged R-hadrons. • Clearly no/poor efficiency for rest lifetimes < 1 ns independently of any selection optimization. • In the next 2 slides, properties of the generated R-hadrons that are associated to reconstructed tracks. Not applied yet any selection cut.

  12. “Reconstructable” charged R-hadrons: Properties I pT nSCT 1 ns R-hadrons are reconstructed also at lower SCT hits than normal. p 1 ns R-hadrons are reconstructed if they are more boosted

  13. “Reconstructable” charged R-hadrons: Properties II dE/dx mass 1 ns R-hadrons has broader mass distribution, Consequence of the high-p boost selection.

  14. Event Selection Cuts have been revised to optimize S/√B and populate the bkg samples. • Event level • Trigger: EF_xe80T_tclcw_loose • GRL* • offline confirmation of the MET trigger: EtmissRefFinal > 130 GeV(was 80) • at least 1 primary vertex (PV) with at least 5 tracks • SUSY recommended event cleaning (A-G)data12_8TeV.periodAllYear_DetStatus-v54-pro13-04_DQDefects-00-00-33_PHYS_StandardGRL_All_Good.xml (H-L)data12_8TeV.periodAllYear_DetStatus-v61-pro14-02_DQDefects-00-01-00_PHYS_StandardGRL_All_Good.xml

  15. Metastable R-hadrons: MET@generation gluino 600 Neutralino 500: Met ~ 90 GeV All the energy of the neutralinos escape, but there are 2 gluinos back-to-back. When the neutralino is very light, there is ymuch more MET, because there are high pt jets coming out at random angles, and the escaping pt does not cancel on the two sides. gluino 600 Neutralino 100: Met ~ 220 GeV

  16. Metastable R-hadrons: MET@afterTrigger gluino 600 Neutralino 500: Met ~ 90 GeV gluino 600 Neutralino 100: Met ~ 220 GeV

  17. Event Selection Cuts have been revised to optimize S/√B and populate the bkg samples. • Event level • Trigger: EF_xe80T_tclcw_loose • GRL* • offline confirmation of the MET trigger: Etmiss RefFinal > 130 GeV (was 80) • at least 1 primary vertex (PV) with at least 5 tracks • SUSY recommended event cleaning • Track Level (at least one track with) • High-pT: pT>80 GeV, primary, n.Pixel hits >=3, nBLayer hits >=1 and n.SCT hits >=4 (was 6 in stable) • Isolated: no primary with pT>1 GeV in a cone of radius ΔR<0.25 • Electron veto, • p-cuts: p>150 GeV & Δp/p<50% (was p>100 GeV) • High ionization: dE/dx > 1.800 - 0.055|η|+ 0.129|η|2 -0.037|η|3 MeV/g cm-2

  18. Metastable R-hadrons: pT of skimmed tracks gluino 600 Neutralino 500: Lower momentum if gluino is unstable because R-hadron is not reconstructed. Close only if lifetime is 10 ns, mainly is X0 is light (there might be other high-p charged tracks in the decay) gluino 600 Neutralino 100:

  19. Metastable R-hadrons: dE/dx of skimmed tracks gluino 600 Neutralino 500: Visible that for short lifetime there is less contribution of R-hadrons (high ionization) gluino 600 Neutralino 100:

  20. Cut flow for 600 GeV (meta) stable Rhadrons

  21. Matching with Jets or muon MS 600 100 10 ns 1 ns Rhadron 600 Stable 1 ns 10 ns 600500 MuSpectro: candidate track geometrical matched with a muid Jets only: candidate track geometrical matched with a Jet but not with a muid Others: candidate track geometrical not matched with a Jet or with a muid  For 10 (1) ns lifetimes the pixel-only analysis is the dominating (only) search method.

  22. Outlook for metastable • As for the stable case, study and revise the definition of the background samplesmainly to populate the samples sufficiently. • Bkg1(low ionization) as data but dE/dx <1.8 • Bkg2 (low momentum) as data but p<150 GeV and pT>10 GeV • Next-to-next: • Generate several lifetime samples, as in the disappearing tracks search, http://arxiv.org/pdf/1310.3675v1.pdf • Study systematics. • Show limits vs lifetime and mass • Move to analysis for metastable charginos. • http://arxiv.org/pdf/1310.3675v1.pdf as illustration

  23. Backup C. Gemme – INFN Genova

  24. Cleaning in SUSY • Implemented SUSY cleaning: at the EVENT level • if ((nt->larError)==2) continue; // Removing LAr error events • if ((nt->tileError)==2) continue; // Removing Tile error events • if ((nt->coreFlags&0x40000) != 0) continue; // Remove incomplete events due to TTC reset larError, tileError and coreFlagsNOT SQUEEZED yet. • // TTileTripReader::checkEvent(unsigned int run, unsigned intlbn, unsigned int event) \\Tile trips in periods G-J ????? Also information are missing in SUSY instructions • recommend to veto events which have any jet pt>40 && & BCH_CORR_JET > 0.05 && DeltaPhi(MET,Jet)<0.3  cuts 10% of GRL events • and with any looser (=BadlooseMinus, 0.15% of jets) jets with pt>20 GeV and any eta  cuts <1% of GRL events (SIMILAR TO THE JET Cleaning that we have used in the candidates events in 2011)

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